In recent years, communication systems' performance and capabilities have continued to improve rapidly in light of several technological advances and improvements with respect to telecommunication network architecture, signal processing, and protocols. In the area of wireless communications, various multiple access standards and protocols have been developed to increase system capacity and accommodate fast-growing user demand. These various multiple access schemes and standards include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), and Orthogonal Frequency Division Multiple Access (OFDMA), etc. Generally, in a system which employs TDMA technique, each user is allowed to transmit information in his assigned or allocated time slots whereas an FDMA system allows each user to transmit information on a particular frequency that is assigned to that particular user. A CDMA system, in contrast, is a spread spectrum system which allows different users to transmit information at the same frequency and at the same time by assigning a unique code to each user. In an OFDMA system, a high-rate data stream is split or divided into a number of lower rate data streams which are transmitted simultaneously in parallel over a number of subcarriers (also called subcarrier frequencies herein). Each user in an OFDMA system is provided with a subset of the available subcarriers for transmission of information.
Code division multiple access (CDMA) technology was introduced in cellular systems in the early 1990s with the development of the IS-95 standard. The IS-95 system has significantly evolved and matured in the last decade resulting in the enhanced revisions IS-95 A and B in 1994 and 1998, respectively. The IS-95-A/B and several related standards form the basis of the second generation cellular technology which is also known as cdmaOne.
The 3G evolution of cdmaOne consists of a family of standards, known as cdma2000, which first appeared with the publication of the IS-2000 Release 0 in 1999. Release A version of IS-2000 was published in mid 2000 with the inclusion of additional signaling support for features such as new common channels, QoS negotiation, enhanced authentication, encryption and concurrent services. The cdma2000 system was designed to be backward compatible with existing cdmaOne networks and voice terminals.
The IS-2000 standard introduces several new features as compared to second-generation (2G) wireless systems. Among those, the introduction of fast forward power control, QPSK modulation, lower code rates, powerful turbo coding, pilot-aided coherent reverse link and support for transmit diversity are considered the major capacity enhancing features in IS-2000.
Even though the IS-2000 standard introduces new features that significantly improve voice capacity and data services, the design was not optimized for high speed IP traffic. As a result, a major addition to cdma2000 was accomplished by the introduction of the high rate packet data (HRPD) system (IS-856) by the end of 2000. The IS-856 standard, also referred to as 1.times.EV-DO herein, is optimized for wireless high-speed packet data services. The IS-856 forward link uses time-division-multiplexed (TDM) waveform, which eliminates power sharing among active users by allocating full sector power and all code channels to a single user at any instant. This is in contrast to code-division-multiplexed (CDM) waveform on the IS-95 forward link, where there is always an unused margin of transmit power depending on the number of active users and power allocated to each user. Each channel (Pilot, Sync, Paging and Traffic channels) in IS-95 is transmitted the entire time with a certain fraction of the total sector power, while the equivalent channel in IS-856 is transmitted, at full power, only during a certain fraction of time.
Due to the TDM waveform of the IS-856 forward link, a terminal is allocated the full sector power whenever it is served, thus no power adaptation is needed. Rather, rate adaptation is used on the IS-856 forward link. In general, the highest data rate that can be transmitted to each terminal is a function of the received SINR from the serving sector. This is typically a time-varying quantity, especially for mobile users. In order to achieve the highest data rate at each time of transmission, each terminal predicts the channel condition over the next packet for its serving sector based on the correlation of the channel states. It selects the highest data rate that can be reliably decoded based the predicted SINR, and then inform the serving sector its selected rate over the reverse link feedback channel. Whenever the network decides to serve a terminal, it transmits at the most recent selected rate fed back from the terminal. This procedure is referred to as closed-loop rate control.
In a system which employs TDM scheduling for transmission from a base station to user terminals or user stations (e.g., the current 1.times.EV-DO downlink or forward link transmission), the base station transmits a single packet to a particular user at any given time. As shown in FIG. 1, different users are time-division multiplexed, i.e., served at different points in time. In order to maintain fairness, the system spends a significant amount of time serving users with low SINR. The TDM scheduling forces the base station to allocate bandwidth among different users in the same proportion in which it allocates its transmit power to different users. While users in poor coverage require a large share of base station transmit power, they need only a small fraction of the bandwidth. While the users with low SINR are being served, the system bandwidth is unnecessarily wasted or underutilized. As a result, the system throughput is significant reduced by the presence of a few users with low SINR (poor coverage).
One approach to addressing the above problem is to use the CDM approach, which is to allocate a variable number of code channels to different users, and apply power control to the transmission to multiple users in order to maintain a reliable link to each user. This approach, however, requires dynamic allocation of code channels to different users, as well as the need to control the power of the different users rapidly enough to track channel variation. Moreover, it turns out that any form of bandwidth-partitioning among multiple users on the downlink is sub-optimal, from the viewpoint of throughput optimization. As a result, the CDM approach does not provide as much gain in system throughput.
There is therefore a need in the art for a method, apparatus, and system for efficient data transmission and processing in a wireless communication environment to improve system throughput and bandwidth utilization.